This application claims the priority of German patent document 100 22 113.0, filed May 6, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a hybrid drive for a motor vehicle having both an internal combustion engine and at least one electric machine as propulsion units.
In addition to the internal combustion engine and the at least one electrical machine, a hybrid drive includes at least one first electrical accumulator which electrically couples the electric machine to an electrical energy supply; an electronic control device automatically operates the at least one electric machine as an electric motor, which is fed with electricity from the accumulator, or as an electric generator for supplying current to the accumulator, as a function of predetermined operating conditions of the motor vehicle.
A hybrid drive of this type disclosed in German patent document DE 196 00 252 A1 contains an exhaust gas turbogenerator for recovering exhaust gas energy, which is used to generate electrical energy. The internal combustion engine can be provided with mechanical supercharging.
xe2x80x9cMechanical superchargingxe2x80x9d takes place by means of a supercharger which is mechanically driven, for example directly from the internal combustion engine via an electrically actuated magnetic clutch, as is known from the specialist book xe2x80x9cFachkunde Kraftfahrzeugtechnikxe2x80x9d (Specialist motor vehicle technology information) 26th Edition, 1999, Europa No. 20108, ISBN 3-8085-2066-3, Page 376.
In hybrid drives, electrical machines serving as vehicle drive sources can be connected in series or in parallel with the internal combustion engine, in order to support the drive power of the latter or to drive the motor vehicle independently of the internal combustion engine. It is known, for example, for the internal combustion engine to drive the wheels of one vehicle axle, while a plurality of electrical machines drive the wheels of another vehicle axle. The electrical machines can also be operated, alternatively, as generators for electricity generation; for this purpose, they can be driven by the vehicle wheels and/or by the internal combustion engine, depending on the embodiment. In order to retard the motor vehicle, it is therefore possible to use not only the vehicle brakes but also the internal combustion engine and the electrical machines. Hybrid drives are, for example, known from U.S. Pat. No. 5,713,425 and German patent documents DE 40 04 330 C2, DE 44 07 666 A1, DE 35 42 059 C1 and DE 41 24 479 A1.
Internal combustion engines with exhaust gas turbochargers and an electrical machine which can be driven by the exhaust gas turbocharger for electricity generation are known from European patent documents EP 0 141 634 A2, and EP 0 223 119 B1, and Japanese patent documents JP 0090163505 AA and JP 0100252517 AA.
One object of the present invention is to simplify hybrid drives of the type mentioned at the beginning.
Another object of the invention is to make such drives more cost-effective.
Still another object of the invention is to increase the efficiency of such drives.
These and other objects and advantages are achieved by the hybrid drive according to the invention, in which at least one exhaust gas turbocharger for the delivery of fresh gas to the internal combustion engine is provided via at least one second electrical machine, which can be operated as an electrical generator. The electric machine is also connected for drive purposes to the rotor of the exhaust gas turbocharger, which is electrically coupled to the accumulator for current supply and to the control device for control purposes. The control device is configured to regulate the supercharge pressure of the internal combustion engine as a function of predetermined operating conditions, and limits the supercharge pressure of the fresh gas generated by the exhaust gas turbocharger by regulating the electrical power of the at least one second electrical machine.
This configuration provides the following advantages: First, it simplifies the hybrid drive, in particular because no bypass valves are necessary on the exhaust gas turbocharger to avoid excessive internal combustion engine supercharge pressures. Also, the electrical machine of the exhaust gas turbocharger can be controlled, in a simple manner by way of open or closed loop control, by the same control device which controls the at least one electrical machine that serves as a vehicle drive source.
Furthermore, the efficiency of the hybrid drive is improved because the electrical accumulator is always optimally charged. This is because the first electrical machine, which serves as a vehicle drive source, generates current during vehicle deceleration procedures and the second electrical machine driven by the exhaust gas turbocharger always generates particularly large amounts of current at a time offset to the above when the internal combustion engine is rotating at high speed. The first electrical machine or the second electrical machine therefore supplement each other in an optimum manner. There is, therefore, always sufficient electrical power available from the accumulator for the at least one first electrical machine that serves as the vehicle drive source, even in the case of a stop-and-go driving operation in the city. Thus, the motor vehicle can be driven away in each case, without using the internal combustion engine, and with only the at least one first electrical machine as the electrical vehicle drive motor, without danger of the electrical accumulator""s being excessively depleted. In the present case, electrical accumulator means any electrical storage unit, in particular batteries and capacitors.
Limiting the supercharge pressure of the exhaust gas turbocharger, by maintaining the rotational speed of the turbine at high output in generator operation, permits a recovery of energy which can then be fed in-phase to the electrical vehicle drive unit or made available to the accumulator.
The at least one second electric machine can preferably be operated not only as a generator but also as an electric motor; and the control device for its operation as a motor is configured as a function of predetermined operating conditions. In consequence, the exhaust gas turbocharger can be driven in the lower rotational speed range, when only a little exhaust gas (or exhaust gas energy) is available, by the second electrical machine acting as an electric motor. In addition, so-called xe2x80x9cturbolagxe2x80x9d can be avoided by the second electrical machine, operated as a motor, accelerating the turbocharger when the latter cannot follow rapid changes in the accelerator pedal positions because of a lack of sufficient exhaust gases or exhaust gas energy. For this purpose, the accelerator pedal is electrically coupled to the control device so that the latter can accelerate the second electrical machine (and therefore the exhaust gas turbocharger) in the case of sudden changes to the accelerator pedal position.
The at least one second electrical machine, operated as a generator, can supply the on-board network of the motor vehicle with electricity.
According to a preferred embodiment of the invention, a drive direct current network is provided to which the accumulator is connected and to which the at least one first electric machine and the at least one second electric machine are each connected by means of a power electronics circuit. The power electronics circuit inverts the DC voltage of the accumulator into an AC voltage required by the electrical machines; and, vice versa, it converts an AC voltage generated by these electrical machines into a DC voltage for the accumulator.
According to a likewise preferred embodiment of the invention, the accumulator (and therefore also the drive direct current network) has an electrical DC voltage of at least 100 V, preferably an electrical DC voltage in the range between 200 V and 350 V. Compared with a now usual lower voltage such, for example, as 6 V, 12 V or 24 V, the substantially higher voltage has the advantage that the electrical currents are substantially lower for the same electrical power. This leads to a distinct reduction in the electrical current heat losses in the lines, components and units and, in consequence, to an improvement in the overall efficiency.
In consequence, smaller electronic components can also be used for the power electronics for transmitting electrical power and for converting direct current into alternating current and vice versa. More highly powered electric machines can therefore also be used. The electric machines are preferably three-phase alternating current machines.